Implant Feedthrough Grounding Structure for Hermetic EMI Filtering
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Solution Overview
Problem
Existing hermetic terminal subassemblies for implantable medical devices face challenges such as biocompatibility, resistance to degradation under applied bias, and susceptibility to electromagnetic interference (EMI) and MRI-induced RF currents, which can lead to device malfunction and tissue damage.
Innovation Solution
The proposed solution involves a feedthrough subassembly with a co-fired insulator substrate assembly, including an alumina insulator body, via holes, and a composite fill of ceramic reinforced metal composite and pure platinum, which are co-fired to form a strong monolithic structure. This structure includes perimeter metallization, a ferrule, and braze seals to ensure hermeticity and electrical connectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional hermetic terminal subassemblies are used, then hermeticity is achieved, but susceptibility to EMI and MRI-induced RF currents occurs
Solution Approach 1:
The patent employs a composite fill material consisting of sintered metal particles (such as silver, copper, or aluminum) combined with glass frit or ceramic binder. This composite structure provides both hermetic sealing and electromagnetic shielding properties, resolving the contradiction between maintaining hermeticity and preventing EMI susceptibility. The conductive metal particles create electromagnetic barriers while the glass/ceramic matrix ensures hermetic sealing.
Solution Approach 2:
The patent modifies the material composition and structural parameters of the feedthrough assembly by incorporating multiple layers with different properties (conductive layers, dielectric layers, magnetic shielding layers). By changing the parameters of individual layers (thickness, conductivity, permeability) and their arrangement, the assembly achieves both hermeticity and EMI resistance simultaneously.
2Reliability
If hermetic terminal subassemblies are used, then electrical isolation is achieved, but MRI-induced heating and tissue damage risk increases
Solution Approach 1:
The patent incorporates magnetic shielding materials (such as mu-metal or ferrite layers) within the composite structure of the feedthrough assembly. These materials have high magnetic permeability that redirects MRI-induced RF currents around sensitive components rather than allowing them to concentrate and heat tissues, thus maintaining electrical isolation while reducing MRI-induced heating risks.
Solution Approach 2:
The patent introduces intermediary shielding layers and grounding structures between the hermetic seal and the external environment. These intermediary elements act as barriers that intercept and dissipate MRI-induced RF energies before they can cause harmful heating, while preserving the electrical isolation function of the hermetic seal.
3Reliability
If ceramic insulator body is used, then hermetic sealing is achieved, but brittleness and catastrophic failure risk occur
Solution Approach 1:
The patent replaces monolithic ceramic with a composite structure where sintered metal particles are embedded in a glass frit or ceramic matrix. This composite fill material provides hermetic sealing similar to traditional ceramic but with enhanced toughness and damage tolerance due to the ductile metal particles and flexible glass binder, preventing catastrophic brittle failure.
Solution Approach 2:
The patent applies different material properties to different regions of the feedthrough assembly. The fill material uses a composite of metal particles and glass/ceramic binder that provides local flexibility and damage tolerance, while maintaining hermetic sealing properties in the sealed regions. This local differentiation of material quality reduces overall brittleness while preserving hermeticity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a hermetic seal with a leak rate no greater than 1 x 10^-7 std cc He/sec, ensuring biocompatibility and resistance to degradation, while also effectively filtering out high-frequency EMI and mitigating MRI-induced heating, thus enhancing the reliability and safety of implantable medical devices.
Implementation Method 1
a hermetic seal hermetically sealing the alumina insulator body to the ferrule opening
Implementation Method 2
a perimeter braze between either the perimeter metallization or the perimeter ceramic reinforced metal composite and the conductive ferrule body, the perimeter braze forming a hermetic seal hermetically sealing the alumina insulator body to the ferrule opening
Implementation Method 3
effectively filtering out high-frequency EMI
Implementation Method 4
an alumina insulator body, via holes, and a composite fill of ceramic reinforced metal composite and pure platinum, which are co-fired to form a strong monolithic structure
Data Source
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AI summary
A feedthrough subassembly attachable to an active implantable medical device includes an electrically conductive grounding path between a first end located on the device side and configured to electrically connect with a plurality of ground electrode plates of a device side capacitor and a second end electrically connected to a ferrule. The grounding path may be one of the following options: a grounded via hole and a plurality of insulator ground plates disposed within the insulator body; a grounding fill at least partially disposed within the grounding via hole including an exposed side portion; a peninsula structure formed as part of the conductive ferrule body extending into the ferrule opening; a grounding composite fill disposed within a grounding recess including an exposed side; a perimeter braze extending into a grounding recess forming a braze channel; and a metallic clip disposed within a grounding recess and electrically contacting a braze channel.